If I turned back the clock 100 years to Nov. 3, 1906, and happened to be sitting, surrounded by psychiatrists in a small stone auditorium in the village of Tubingen, Germany, I might see on the program the name of a speaker, Dr. Alois Alzheimer.
Alzheimer actually spoke in this German auditorium in 1906, and he described a patient named "Augusta" who, in her middle 50s, had developed the seemingly unfounded delusion that her husband was unfaithful.
This delusion blossomed into full-fledged paranoid psychosis, and Alzheimer continued to care for Augusta in the hospital until she died.
Alzheimer then personally conducted her autopsy.
During the autopsy, he noticed something very wrong with Augusta's brain, which he called "a peculiar disease of the cerebral cortex."
Alzheimer used that phrase as the title of his presentation at Tubingen.
He had thought, at the time, that Augusta's "peculiar disease" was a rarity.
But, in fact, half of our current population older than the age of 85 is affected by the same disease.
Today, we call it Alzheimer's disease.
Alzheimer might be astonished to learn that nursing homes and psychiatric hospitals in developed nations have gradually filled with millions of patients suffering from the still-baffling illness that now carries his name.
Doctors didn't often use the diagnosis of Alzheimer's disease until very recently.
The syndrome of dementia -- literally, the loss of the ability to think or mentate -- was long blamed on the narrowing of blood vessels in the brain, but the narrowing blood vessels weren't severe enough to explain the problems with thought and reasoning.
Over time, though, medicine evolved and people lived longer.
As life span increased, and as the brains of our elders began to be examined, two things happened.
First, highly functional 80- and 90-year-olds -- think pianist Vladimir Horowitz or cellist Pablo Casals -- defied the myth that late-life brain failure was inevitable; in other words, dementia wasn't something that "normally" happened, doctors realized.
Then, by comparing patients' medical histories with their autopsies, doctors realized that the brains from most elderly patients with dementia were "gunked up" with abnormal proteinlike structures, both inside and outside nerve cells.
That gunk between nerve cells, called amyloid plaque, is now considered one sign of Alzheimer's disease.
So, doctors gradually began to recognize the disease, but the truth is, doctors aren't certain that these plaques cause Alzheimer's disease, and doctors don't know what usually causes those plaques.
In some ways, Alzheimer's disease is still a mystery, much as it was 100 years ago.
Dr. Sam Gandy is a professor and director at the Farber Institute for the Neurosciences of Thomas Jefferson University in Philadelphia. Gandy is also chair of the Alzheimer Association's National Medical and Scientific Advisory Council.
OK, then, so, what do doctors and scientists know for sure about Alzheimer's?
Certainly, several things happen in the brain before the first signs of Alzheimer's appear:
Levels of a key brain chemical plummet: The technical name for this substance is acetylcholine.
Levels of two substances rise: The technical names are amyloid and tau.